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RFC 2524

Informational
Pages: 83
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Neda's Efficient Mail Submission and Delivery (EMSD) Protocol Specification Version 1.3

Part 1 of 4, p. 1 to 11
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Network Working Group                                         M. Banan
Request for Comments: 2524                   Neda Communications, Inc.
Category: Informational                                  February 1999


                                 Neda's
             Efficient Mail Submission and Delivery (EMSD)
                   Protocol Specification Version 1.3

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1999).  All Rights Reserved.

IESG Note

   The protocol specified in this document may be satisfactory for
   limited use in private wireless IP networks.  However, it is
   unsuitable for general-purpose message transfer or for transfer of
   messages over the public Internet, because of limitations that
   include the following:

   - Lack of congestion control

      EMSD is layered on ESRO [RFC 2188], which does not provide
      congestion control.  This makes EMSD completely unsuitable for
      end-to-end use across the public Internet.  EMSD should be
      considered for use in a wireless network only if all EMSD email
      exchanged between the wireless network and the public Internet
      will transit an EMSD<->SMTP gateway between the two regions.

   - Inadequate security

      The document specifies only clear-text passwords for
      authentication.  EMSD should be used across a wireless network
      only if sufficiently strong encryption is in use to protect the
      clear-text password.

   - Lack of character set internationalization

      EMSD has no provision for representation of characters outside of
      the ASCII repertoire or for language tags.

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   - Poorly defined gatewaying to and from Internet Mail

      Because Internet Mail and EMSD have somewhat different and
      conflicting service models and different data models, mapping
      between them may provide good service only in limited cases, and
      this may cause operational problems.

   The IESG therefore recommends that EMSD deployment be limited to
   narrow circumstances, i.e., only to communicate with devices that
   have inherent limitations on the length and format of a message (no
   more than a few hundred bytes of ASCII text), using either:

   a. wireless links with adequate link-layer encryption and gatewayed
      to the public Internet, or

   b. a private IP network that is either very over-provisioned or has
      some means of congestion control.

   In the near future, the IESG may charter a working group to define an
   Internet standards-track protocol for efficient transmission of
   electronic mail messages, which will be highly compatible with
   existing Internet mail protocols, and which wil be suitable for
   operation over the global Internet, including both wireless and wired
   links.

ABSTRACT

   This document specifies the protocol and format encodings for
   Efficient Mail Submission and Delivery (EMSD). EMSD is a messaging
   protocol that is highly optimized for submission and delivery of
   short Internet mail messages.  EMSD is designed to be a companion to
   existing Internet mail protocols.

   This specification narrowly focuses on submission and delivery of
   short mail messages with a clear emphasis on efficiency.  EMSD is
   designed specifically with wireless network (e.g., CDPD, Wireless-IP,
   Mobile-IP) usage in mind.  EMSD is designed to be a natural
   enhancement to the mainstream of Internet mail protocols when
   efficiency in mail submission and mail delivery are important.  As
   such, EMSD is anticipated to become an initial basis for convergence
   of Internet Mail and IP-based Two-Way Paging.

   The reliability requirement for message submission and message
   delivery in EMSD are the same as existing email protocols.  EMSD
   protocol accomplishes reliable connectionless mail submission and
   delivery services on top of Efficient Short Remote Operations (ESRO)
   protocols as specified in RFC-2188 [1].

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   Most existing Internet mail protocols are not efficient.  Most
   existing Internet mail protocols are designed with simplicity and
   continuity with SMTP traditions as two primary requirements.  EMSD is
   designed with efficiency as a primary requirement.

   The early use of EMSD in the wireless environment is manifested as
   IP-based Two-Way Paging services.  The efficiency of this protocol
   also presents significant benefits for large centrally operated
   Internet mail service providers.

Table of Contents

   1  PRELIMINARIES                                                 4
      1.1 Internet Mail Submission and Delivery     .   .   .   .   4
      1.2 Relationship Of EMSD To Other Mail Protocols  .   .   .   5
      1.3 EMSD Requirements and Goals   .   .   .   .   .   .   .   7
      1.4 Anticipated Uses Of EMSD  .   .   .   .   .   .   .   .   8
      1.5 Definitions of Terms Used in this Specification   .   .   9
      1.6 Conventions Used In This Specification    .   .   .   .   9
      1.7 About This Specification  .   .   .   .   .   .   .   .  10
   2  EFFICIENT MAIL SUBMISSION AND DELIVERY OVERVIEW              10
   3  EFFICIENT MAIL SUBMISSION AND DELIVERY PROTOCOL              11
      3.1 Use Of Lower Layers   .   .   .   .   .   .   .   .   .  13
          3.1.1 Use of ESROS    .   .   .   .   .   .   .   .   .  13
          3.1.2 Use Of UDP  .   .   .   .   .   .   .   .   .   .  13
          3.1.3 Encoding Rules  .   .   .   .   .   .   .   .   .  13
          3.1.4 Presentation Context    .   .   .   .   .   .   .  14
      3.2 EMSD-UA Invoked Operations    .   .   .   .   .   .   .  14
          3.2.1 submit  .   .   .   .   .   .   .   .   .   .   .  14
          3.2.2 deliveryControl     .   .   .   .   .   .   .   .  17
          3.2.3 deliveryVerify  .   .   .   .   .   .   .   .   .  21
      3.3 EMSD-SA Invoked Operations    .   .   .   .   .   .   .  23
          3.3.1 deliver     .   .   .   .   .   .   .   .   .   .  23
          3.3.2 submissionControl   .   .   .   .   .   .   .   .  25
          3.3.3 submissionVerify    .   .   .   .   .   .   .   .  28
      3.4 EMSD Common Information Objects   .   .   .   .   .   .  30
          3.4.1 SecurityElements    .   .   .   .   .   .   .   .  30
          3.4.2 Message Segmentation and Reassembly     .   .   .  30
          3.4.3 Common Errors   .   .   .   .   .   .   .   .   .  33
          3.4.4 ContentType     .   .   .   .   .   .   .   .   .  35
          3.4.5 EMSDMessageId   .   .   .   .   .   .   .   .   .  35
          3.4.6 EMSDORAddress   .   .   .   .   .   .   .   .   .  36
          3.4.7 EMSDAddress     .   .   .   .   .   .   .   .   .  36
          3.4.8 DateTime    .   .   .   .   .   .   .   .   .   .  36
          3.4.9 AsciiPrintableString    .   .   .   .   .   .   .  37
          3.4.10 ProtocolVersionNumber  .   .   .   .   .   .   .  37
      3.5 Submission and Delivery Procedures    .   .   .   .   .  38
   4  DUPLICATE OPERATION DETECTION SUPPORT                        40

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      4.1 Duplicate Operation Detection Support Overview    .   .  40
          4.1.1 Operation Value     .   .   .   .   .   .   .   .  40
          4.1.2 Operation Instance Identifier   .   .   .   .   .  41
   5  EMSD PROCEDURE FOR OPERATIONS                                42
      5.1 MTS Behavior  .   .   .   .   .   .   .   .   .   .   .  43
          5.1.1 MTS Performer   .   .   .   .   .   .   .   .   .  43
          5.1.2 Message-submission  .   .   .   .   .   .   .   .  44
          5.1.3 Delivery-control    .   .   .   .   .   .   .   .  46
          5.1.4 Delivery-verify     .   .   .   .   .   .   .   .  46
          5.1.5 MTS Invoker     .   .   .   .   .   .   .   .   .  46
      5.2 UA Behavior   .   .   .   .   .   .   .   .   .   .   .  49
          5.2.1 UA Performer    .   .   .   .   .   .   .   .   .  49
          5.2.2 UA Invoker  .   .   .   .   .   .   .   .   .   .  52
   6  EMSD FORMAT STANDARDS                                        54
      6.1 Format Standard Overview  .   .   .   .   .   .   .   .  54
      6.2 Interpersonal Messages    .   .   .   .   .   .   .   .  54
          6.2.1 Heading fields  .   .   .   .   .   .   .   .   .  55
          6.2.2 Body part types     .   .   .   .   .   .   .   .  61
   7  ACKNOWLEDGMENTS                                              62
   8  SECURITY CONSIDERATIONS                                      62
   9  AUTHOR'S ADDRESS                                             62
   A. EMSD-P ASN.1 MODULE                                          63
   B. EMSD-IPM ASN.1 MODULE                                        74
   C. RATIONALE FOR KEY DESIGN DECISIONS                           78
      C.1 Deviation From The SMTP Model     .   .   .   .   .   .  78
          C.1.1 Comparison of SMTP and EMSD Efficiency  .   .   .  78
      C.2 Use of ESRO Instead of TCP    .   .   .   .   .   .   .  79
      C.3 Use Of Remote Procedure Call (RPC) Model  .   .   .   .  79
      C.4 Use Of ASN.1  .   .   .   .   .   .   .   .   .   .   .  80
   D. FURTHER DEVELOPMENT                                          81
   E. REFERENCES                                                   82
   F. FULL COPYRIGHT STATEMENT                                     83

1  PRELIMINARIES

   Mail in the Internet was not a well-planned enterprise, but instead
   arose in more of an "organic" way.

   This introductory section is not intended to be a reference model and
   concept vocabulary for mail in the Internet.  Instead, it only
   provides the necessary preliminaries for the concepts and terms that
   are essential to this specification.

1.1  Internet Mail Submission and Delivery

   For the purposes of this specification, mail submission is the
   process of putting mail into the mail transfer system (MTS).

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   For the purposes of this specification, mail delivery is the process
   of the MTS putting mail into a user's final mail-box.

   Throughout the Internet, presently most of mail submission and
   delivery is done through SMTP.

   SMTP was defined as a message *transfer* protocol, that is, a means
   to route (if needed) and deliver mail by putting finished (complete)
   messages in a mail-box.  Originally, users connected to servers from
   terminals, and all processing occurred on the server.  Now, a split-
   MUA (Mail User Agent) model is common, with MUA functionality
   occurring on both the user's own system and the server.

   In the split-MUA model, getting the messages to the user is
   accomplished through access to a mail-box on the server through such
   protocols as POP and IMAP. In the split-MUA model, user's access to
   its message is a "Message Pull" paradigm where the user is required
   to poll his mailbox.  Proper message delivery based on a "Message
   Push" paradigm is presently not supported.  The EMSD protocol
   addresses this shortcoming with an emphasis on efficiency.

   In the split-MUA model, message submission is often accomplished
   through SMTP. SMTP is widely used as a message *submission* protocol.
   Widespread use of SMTP for submission is a reality, regardless of
   whether this is good or bad.  EMSD protocol provides an alternative
   mechanism for message submission which emphasizes efficiency.

1.2  Relationship Of EMSD To Other Mail Protocols

   Various Internet mail protocols facilitate accomplishment of various
   functions in mail processing.

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   Figure 1, categorizes the capabilities of SMTP, IMAP, POP and EMSD
   based on the following functions:

   +------------------+------+-------+-----+------+
   |         Protocols| SMTP |  IMAP | POP | EMSD |
   |Functions         |      |       |     |      |
   |------------------|------|-------|-----|------|
   |Submission        | XX   |       |     | XXX  |
   |------------------|------|-------|-----|------|
   |Delivery          | XXX  |       |     | XXX  |
   |------------------|------|-------|-----|------|
   |Relay (Routing)   | XXX  |       |     |      |
   |------------------|------|-------|-----|------|
   |Retrieval         |      |  XXX  | XXX |  XX  |
   |------------------|------|-------|-----|------|
   |Mailbox Access    |      |  XXX  |  X  |      |
   |------------------|------|-------|-----|------|
   |Mailbox Synch.    |      |  XXX  |     |      |
   +------------------+------+-------+-----+------+

   Figure 1:  Messaging Protocols vs.  Supported Functions


     o Mail Submission

     o Mail Delivery

     o Mail Routing (Relay)

     o Mail Retrieval

     o Mail-box Access

     o Mail-box Synchronization

   In Figure 1, the number of "X"es in each box denotes the extent to
   which a particular function is supported by a particular protocol.

   Figure 1 clearly shows that combinations of these protocols can be
   used to complement each other in providing rich functionality to the
   user.  For example, a user interested in highly mobile messaging
   functionalities can use EMSD for "submission and delivery of time
   critical and important messages" and use IMAP for comprehensive
   access to his/her mail-box.

   For mail submission and delivery of short messages EMSD is up to 5
   times more efficient than SMTP both in terms of the number of packets
   transmitted and in terms of number of bytes transmitted.  Even with

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   PIPELINING and other possible optimizations of SMTP, EMSD is up to 3
   times more efficient than SMTP both in terms of the number of packets
   transmitted and in terms of number of bytes transmitted.  Various
   efficiency studies comparing EMSD with SMTP, POP and IMAP are
   available.  See Section C.1.1 for more information about comparison
   of SMTP and EMSD's efficiency.

1.3  EMSD Requirements and Goals

   The requirements and goals driving design of EMSD protocol are
   enumerated below.

    1. Provide for submission of short mail messages with the same level
       of functionality (or higher) that the existing Internet mail
       protocols provide.

    2. Provide for delivery of short mail messages with the same level
       of functionality (or higher) that the existing Internet mail
       protocols provide.

    3. Function as an extension of the existing mainstream Internet
       mail.

    4. Minimize the number of transmissions.

    5. Minimize the number of bytes transmitted.

    6. Be quick:  minimize latency of message submission and delivery.

    7. Provide the same level of reliability (or higher) that the
       existing email protocols provide.

    8. Accommodate varying sizes of messages:  the size of a message may
       determine how the system deals with the message, but the system
       must accommodate it.

    9. Be power efficient and respect mobile platform resources:
       including memory and CPU levels, as well as battery power
       longevity (i.e.  client-light and server-heavy).

    10. Highly extendible:  different users will demand different
        options, so the solution cannot require every feature to be a
        part of every message.  Likewise, usage will emerge that is not
        currently recognized as a requirement.  The solution must be
        extendible enough to handle new, emerging requirements.

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    11. Secure:  provide the same level of security (or higher) that the
        existing email protocols provide.  Content confidentiality,
        originator/recipient authentication and message integrity must
        be available options to users.

    12. Easy to implement:  Re-use existing technology as much as
        possible.

1.4  Anticipated Uses Of EMSD

   Any network and network operator which has significant bandwidth and
   capacity limitations can benefit from the use of EMSD. Any network
   user who must bear high costs for measured network usage can benefit
   from the use of EMSD.

   Initial uses of EMSD is anticipated to be primarily over IP-based
   wireless networks to provide two-way paging services.

   EMSD can also function as an adjunct to Mail Access Protocols for
   "Mail Notification Services".

   Considering:

      o that most wireless networks shall converge toward being IP-
        based;

      o that two-way paging is the main proven application in most
        wide-area wireless networks;

      o that two-way paging industry and the Internet Email industry can
        and should converge based on a set of open protocols that
        address the efficiency requirements adequately;

      o that existing Internet email protocols are not bandwidth
        efficient;

      o that existing Internet email protocols do not properly support
        the "push" model of delivery of urgent messages,

   the EMSD protocol is designed to facilitate the convergence of IP-
   based two-way paging and Internet email.

   Mail submission and delivery take place at the edges of the network.
   More than one mail submission and delivery protocols which address
   requirements specific to a particular user's environment are likely
   to be developed.  Such diversity on the edges of the network is

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   desirable and with the right protocols, this diversity does not
   adversely impact the integrity of the mail transfer system.  EMSD is
   the initial basis for the mail submission and delivery protocol to be
   used when the user's environment demands efficiency.

1.5  Definitions of Terms Used in this Specification

   The following informal definitions and acronyms are intended to help
   describe EMSD model described in this specification.

   Efficient Mail Submission and Delivery Protocol (EMSD-P): The
       protocol used to transfer messages between the EMSD - Server
       Agent (e.g., a Message Center) and the EMSD - User Agent (e.g., a
       Two-Way Pager), see Figure 2.
   Message Transfer Agent (MTA)

   Message Transfer Service (MTS)

   Message Routing Service (MRS): Collection of MTAs responsible for
       mail routing.
   Message User Agent (MUA)

   Efficient Mail Submission Server Agent (EMS-SA): An Application
       Process which conforms to this protocol specification and accepts
       mail from an EMS-UA and transfers it towards its recipients.

   Efficient Mail Delivery Server Agent (EMD-SA): An Application Process
       which conforms to this protocol specification and delivers mail
       to an EMD-UA.
   Efficient Mail Submission and Delivery Server Agent (EMSD-SA): An
       Application Process which incorporates both EMS-SA and EMD-SA
       capabilities.

   Efficient Mail Submission User Agent (EMS-UA): An Application Process
       which conforms to this protocol specification and submits mail to
       EMS-SA.

   Efficient Mail Delivery User Agent (EMD-UA): An Application Process
       which conforms to this protocol specification and accepts
       delivery of mail from EMD-SA.
   Efficient Mail Submission and Delivery User Agent (EMSD-UA): An
       Application Process which incorporates both EMS-UA and EMD-UA
       capabilities.

1.6  Conventions Used In This Specification

   The key words "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", and "MAY"
   in this specification are to be interpreted as defined in [2].

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   This specification uses the ES-OPERATION notation defined in
   Efficient Short Remote Operations (ESRO) protocols as specified in
   RFC-2188 [1].

   Operations and information objects are typically described using the
   ES-OPERATION and ASN.1 notations in the relevant sections of the
   specification.

   The complete machine verifiable ASN.1 modules are also compiled in
   one place in Appendix A and Appendix B.

1.7  About This Specification

   This protocol specification constitutes a point-of-record.  It
   documents information exchanges and behaviors of existing
   implementations.  It is a basis for implementation of efficient mail
   submission and delivery user agents and servers.

   This specification has been developed entirely outside of IETF. It
   has had the benefit of review by many outside of IETF. Much has been
   learned from existing implementations of this protocol.  A number of
   deficiencies and areas of improvement have been identified and are
   documented in this specification.

   This protocol specification is being submitted on October 23, 1998
   for timely publication as an Informational RFC.

   Future development and enhancements to this protocol may take place
   inside of IETF.

2  EFFICIENT MAIL SUBMISSION AND DELIVERY OVERVIEW

   This section offers a high level view of the Efficient Mail
   Submission and Delivery Protocol and Format Standards (EMSD-P&FS).

   The EMSD-P&FS are used to transfer messages between the EMSD - Server
   Agent (e.g., a Message Center) and the EMSD - User Agent (e.g., a
   Two-Way Pager), see Figure 2.

   This specification defines the protocols between an EMSD - User Agent
   (EMSD-UA) and an EMSD - Server Agent (EMSD-SA). The EMSD - P&FS
   consist of two independent components:

    1. EMSD Format Standard (EMSD-FS).

       EMSD-FS is a non-textual form of compact encoding of Internet
       mail (RFC-822) messages which facilitates efficient transfer of
       messages.  EMSD-FS is used in conjunction with the EMSD-P but is

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       not a general replacement for RFC-822.  EMSD-FS defines a method
       of representation of short interpersonal messages.  It defines
       the "Content" encoding (Header + Body).  Although EMSD-FS
       contains end-to-end information its scope is purely point-to-
       point.  EMSD-FS relies on EMSD-P (see 2 below) for the transfer
       of the content to its recipients.

       This is described in the section entitled EMSD Format Standards.

    2. Efficient Mail Submission and Delivery Protocol (EMSD-P).

       EMSD-P is responsible for wrapping an EMSD-FS message (see 1
       above) in a point-to-point envelope and submitting or delivering
       it.  EMSD-P relies on the services of Efficient Short Remote
       Operation Services (ESROS) as specified in RFC-2188 [1] for
       transporting the point-to-point envelope.  Some of the services
       of EMSD-P include:  message originator authentication and
       optional message segmentation and reassembly.  The EMSD-P is
       expressed in terms of abstract services using the ESROS notation.
       This is described in the section entitled Efficient Mail
       Submission and Delivery Protocol.

   It is important to recognize that EMSD-P and EMSD-FS are not end-to-
   end, but focus on the point-to-point transfer of messages.  The two
   points being EMSD-SA and EMSD-UA. EMSD-P function as elements of the
   Internet mail environment, which provide end-to-end (EMSD-User to any
   other Messaging Originator or Recipient) services.

   Figure 2 illustrates how the EMSD-P&FS defines the communication
   between a specific EMSD-UA and a specific EMSD-SA. The Message
   Transfer System may include a number of EMSD-SAs.  Each EMSD-SA may
   have any number of EMSD-UAs with which it communicates.

   The Efficient Mail Submission and Delivery Services use the Efficient
   Short Remote Operation Services (ESROS). They also use the Duplicate
   Operation Detection Support Functions as described in the section
   entitled Duplicate Operation Detection Support Functions.  These
   functions guarantee that an operation is performed no more than once.



(page 11 continued on part 2)

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